Top cap for electron tubes



Aug. 3, 1948. 'E. F. DlLLABY TOP CAP FOR ELECTRON TUB ES Filed April 7,1944 INVENTOR '11 f7. 317/06 ma/ ATTORNEYS Patented Aug. 3, 1948 UNITEDOFFICE TOP GAP FOR ELECTRON TUBES Edwin F. Dillaby, Beverly, Mass,assignor to Bruce A. Cofiin, Peabody, Mass.

Application April 7, 1944, Serial No. 529,915

4 Claims.

This invention relates to an electron tube, more particularly to a topcap for such tube.

In the use of equipment which utilizes an electron tu'be having two topcaps between which a potential is applied, a high voltage breakdown mayoccur between these caps in the rarified-air which is found at highaltitudes, such altitudes being reached with airborne equipment. It isknown that prior .to the occurrence of a discharge between the top caps,a corona is first exhibited at each cap in the vicinity of the largestdiameter of the cap. The largest diameter of the cap is usually adjacentthe contact of the cap with (the glass. The coronas which are exhibitedrapidly change to an arc spanning the distance between the caps and theare usually travels on the surface of the glass. The corona is sometimeslessened by rolling inwardly the edges of the caps which lessens theinitiation of the corona discharge.

One of the objects of this invention is to provide an electron tube withexternal or top caps which may be used at higher altitudes than electrontubes of this character which are at the present time in existence.

Another object of this invention is to provide an electron tube with topcaps between which a high voltage will not break down when in highaltitude.

Another object of this invention is to increase the dielectric along thesurface of the tube at the junction of the caps with the glass envelopeto an extent at least as great as the dielectric of the surrounding airbetween the caps at a point removed from the surface of the tube.

Another object of this invention is to eliminate the formation of acorona at any point along the cap.

With these and other objects in view, the invention consists of certainnovel features of construction, as will be more fully described andparticularly pointed out in the appended claims.

In the accompanying drawings:

Fig. 1 is an elevation of an electron rtube embodying this invention;

Fig. 2 is a sectional view of one of the top caps used in this tubeshown on a greatly enlarged scale;

Fig. 3 is a sectional view showing fragmentally the upper part of thetube with two top caps in position on the tube.

In proceeding with this invention, it is unnecessary to roll in theflaring flange of the sheet metal cups which are utilized for the topcaps. The dielectric path along the glas between the top caps isincreased by imbedding the lower edges 2 of the cups in a low loss resinwhich is molde about the top caps and up into the inside thereof. Thedielectric between the terminals by this arrangement being increased toan extent greater than the dielectric of the air between metallicsurfaces of the terminals. By such irnbedding of t e lower edges of thecaps no coronas are formed about the lower edges of the caps which areusually initiated prior to breakdown or discharge between the caps ofthe tube.

With reference to the drawing HI designate generally an electron tubehaving a base H with a guide I2 and contact pins I3. An envelope M isfixed to the base and has caps [*5 mounted thereon at its top.

Each cap 15 is a drawn sheet metallic cup having a cylindrical side wall1-6 and an integral end wall I1 which is recessed as at l8 and piercedas at IS. A lead in wire 20 is secured to this top Wall I"! by beingpositioned in the opening [9 and soldered in place by solder '2l whichfills the recess l 8 providing a smooth contact or rounded surface 22.

The envelope I4 at the :points of location of the caps 15 bulgesoutwardly as at 25 into the hollow interior of the caps l5.

Each cap 1-5 has a low loss material 26 moulded about it which e-m'bedsthe flaring edge or flange 24 on the cap which is closest to theenvelope I4. This molded material completely embraces this flange 24 andextends up into the interior of the cap to contact with the innersurface of the wall [8 as at 21 and also provides an extension of thecylindrical side wall as at 28 providing a hollow portion bounded by thecylindrical wa11 29, a portion bounded by the cylindrical wall '30 andan inc-lined boundary surface 3| extending between the two. While at theupper end the molded portion tapers inwardly to provide a conicalsurface 33 to the junction with the opening through the top wall as atH).

Each of the caps, complete as shown in Fig. 2, is placed in positionover the bulging portions 25 of the envelope and some filling of acementitious character 35 is positioned in the reces or hollow portionbetween the interior of the cap and the bulging portion 25 for thesecuring of the cap in position. Soldering 0f the lead in wire to thecap takes place after the cap, as shown in Fig. 2, is cemented inposition by the adhesive 35.

The dielectric which is used is any one of the many known low lossmoldable materials, such as thermo-setting resin, pressed steatite, micabonded glass, porcelain, glass, or others.

From the above construction and arrangement larged flanges is greaterthan the dielectric of the air between the metallic parts of the capoutwardly from the tube. The result is such that where satisfactoryoperation previously could only be had at an altitude of forty thousandfeet above sea level with the arrangement here shown satisfactoryoperations may be had in excess of sixty thousand feet above sea level.Thus airborne equipment which requires electron tubes of the type hereshown may be utilized at higher altitudes than heretofore.

1. In an electron discharge device; a glass envelope, a pair of topcaps, each comprising an inverted metallic cup having a top wall and aflaring flange at the free edge of its side wall terminating concentricwith the axis of the cup, and a low loss material molded about saidflange and along the inner surface of the side wall.

2. In an electron discharge device, a top cap, each comprising aninverted metallic cup having a top wall and a flarin flange at the freeedge of its side terminating concentric with the axis of the cup, and alow loss material molded about said flange and along the inner surfaceof the side wall.

3. In an electron discharge device, a top cap comprising a cup of twodifferent diameters, means embracing the portion of said cup of greaterdiameter to eliminate a corona occurring thereabout.

4. A terminal for an electron tube comprising a top cap with aconductive cup having two different diameters, the portion of said cuphaving two different diameters and the portion of said cup :ofgreate-rdiameter being embedded in dielectric material to eliminate a coronaoccurring there about.

EDWIN F. DILLABY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number

